<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>

    <link rel="stylesheet" href="css/bootstrap.min.css">
    <script src="js/jquery-3.4.1.min.js"></script>
    <script src="js/bootstrap.bundle.min.js"></script>
    <script src="js/bootstrap.min.js"></script>

</head>
<body>
        <form  >
                <div class="form-row">
                  <div class="col-md-4 mb-3">
                    <label for="validationCustom01">账户</label>
                    <input type="text" class="form-control is-invalid" id="validationCustom01" placeholder="请输入账户" value="" required>
                    <div class="valid-feedback">
                      Looks good!
                    </div>
                  </div>

                  <hr>
                  
                  <div class="col-md-4 mb-3">
                    <label for="validationCustom02">密码</label>
                    <input type="text" class="form-control is-valid" id="validationCustom02" placeholder="请输入密码" value="" required>

                    <div class="valid-feedback">
                      输入正确
                    </div>
                    
                  </div>
                  <div class="col-md-4 mb-3">
                    <label for="validationCustomUsername">Username</label>
                    <div class="input-group">
                      <div class="input-group-prepend">
                        <span class="input-group-text" id="inputGroupPrepend">@</span>
                      </div>
                      <input type="text" class="form-control" id="validationCustomUsername" placeholder="Username" aria-describedby="inputGroupPrepend" required>
                      
                      <div class="invalid-feedback">
                        输入不对
                      </div>
                    </div>
                  </div>
                </div>
                
                <button class="btn btn-primary" type="submit">Submit form</button>
              </form>
</body>
</html>